Older African-Americans (63%) and Hispanics (70%) are especially vulnerable to spending their golden years in economic peril, the study says, with 48% of all U.S. seniors, or about 19.9 million Americans, "one bad economic shock away" from falling off a financial cliff after age 65 -- a fall from which they may not recover.

The study, Financial Security Of Elderly Americans At Risk, by EPI researchers Elise Gould and David Cooper, says that rising health care costs could be the straw that breaks the proverbial camel's back for Americans in retirement. They also warn Congress that any decline in Social Security or Medicare outlays would likely hurt living standards for U.S. seniors in their 60s, 70s and beyond.

"After working hard their entire lives, millions of our elderly are struggling to pay for basic needs like food, medicine and housing, even with Social Security and Medicare," Gould says. "As such, policy-makers should consider the dire consequences proposals to restructure these programs would have on our parents and grandparents, shifting more costs onto them when many are already barely making ends meet."

Gould and Cooper offer these additional warnings and estimates for U.S. seniors either heading into retirement or there already:

Americans 80 and over are at greatest risk of falling into poverty. The EPI study says that 58% of that group are "economically vulnerable," versus 44.4% of seniors aged 65 to 79.

Women are 10.7 percentage points more likely than men to fall deeply into poverty in retirement (52.6% versus 41.9%).

Facing a weak economic future as a senior largely depends on where you live. For example, the EPI report says that only 35% of North Dakota seniors are at risk for poverty after their working years. But that number rises to 59% for seniors living in or near Washington, D.C.